1. Field of the Invention
The present invention relates to semiconductor radiation detectors and, more particularly, to a semiconductor radiation detector having an improved electrode design.
2. Description of Related Art
With reference to FIGS. 1 and 2, a typical, prior art configuration of a co-planar grid (CPG) radiation detector 1, such as, without limitation, CdxZn1-xTe, (0≦x≦1), detector, includes metal or non-metal conductive electrodes on opposing surfaces. More specifically, a body of radiation detector material 2, e.g., CdxZn1-xTe, (0≦x≦1), has a continuous cathode electrode 4 on one face of body and an anode structure 6 comprised of two sets of elongated conductors 8 and 12 which are interconnected to form two independent, interdigitated grid electrodes on the face of body 2 opposite cathode 4.
Anode structure 6 includes a first anode conductor comprised of a first set of elongated conductors 8 spaced from each other and defining elongated gaps 10 between each pair of adjacent anode conductors 8. Herein, anode conductors 8 are also called “collecting anodes”. Anode structure 6 also includes a second anode conductor comprised of a second set of elongated conductors 12 spaced from each other and defining elongated gaps 14 therebetween. Herein, anode conductors 12 are also called “non-collecting anodes”.
As shown in FIGS. 1 and 2, with the exception of one collecting anode 8 on an end thereof, each collecting anode 8 is disposed in a gap 14 between, desirably intermediate, a pair of adjacent non-collecting anodes 12. Similarly, with the exception of one non-collecting anode 12 on an end thereof, each non-collecting anode 12 is positioned in a gap 10 between, desirably intermediate, a pair of adjacent collecting anodes 8. Desirably, adjacent collecting and non-collecting anodes 8 and 10 are separated from each other by a gap 21. However, this is not to be construed as limiting the invention since the gap between each pair of adjacent collecting and non-collecting anodes 8 and 12 can be any suitable and/or desirable distance deemed suitable and/or desirable by one of ordinary skill in the art.
All of the collecting anodes 8 can be coupled to an optional collecting bond pad 16 either directly or by way of a lateral conductor 18. Similarly, all of the non-collecting anodes 12 can be connected to an optional non-collecting bond pad 20 either directly or by way of a lateral conductor 22. Optional bond pads 16 and 20 can be utilized to facilitate connecting collecting anodes 8 and non-collecting anodes 12 to suitable electrical biases (not shown).
Anode structure 6 can be surrounded by an optional guard ring 24 as is known in the art. Lastly, radiation detector 1 desirably includes on the sides thereof an insulator 26. Desirably, insulator 26 is also disposed in the gaps 21 between adjacent pairs of collecting and non-collecting anodes 8 and 12 as well as between guard ring 24 and either a collecting anode 8, a non-collecting anode 12, lateral conductor 18 or lateral conductor 22, as the case may be. The portion of insulator 26 on the sides of body 2 can be the same or different than the portion of insulator 26 on the surface of body 2 that includes anode structure 6. For example, insulator 26 can be an insulating paint well-known in the art, or an insulator deposited by evaporation or sputtering, such as AlN, Al2O3 or Si3N4. However, this is not to be construed as limiting the invention since it is envisioned that the insulator on the sides of body 2 and/or the insulator on the surface of body 2 including anode structure 6 can be any insulator deemed suitable and/or desirable by one of ordinary skill in the art.
In use of detector 1, a cathode bias voltage (a negative high voltage) is applied across the detector to cause electrons occurring in body 2 in response to ionizing radiation impinging on body 2 to drift toward anode structure 6. Additional bias voltages are applied between collecting anodes 8 and non-collecting anodes 12 of anode structure 6 whereupon electrons in body 2 are steered toward collecting anodes 8. This additional bias is small compared to the bias applied to cathode 4, such that most of the volume of body 2 experiences a linear electric field. Desirably, only very near collecting anodes 8 and non-collecting anodes 12 is the electric field bent toward collecting anodes 8.
Factors that affect the performance of radiation detector 1 include material uniformity, charge transport properties, bulk resistivity, surface passivation and the design of anode structure 6.
Information regarding prior art radiation detectors can be found in U.S. Pat. Nos. 5,530,249; 5,777,338; and 6,043,106, in an article by P. N. Luke, entitled “Unipolar Charge Sensing With Coplanar Electrodes-Application To Semiconductor Detectors”, IEEE Trans. Nucl. Sci., Vol. 42, No. 4, pp. 207-213, August 1995 and in an article by P. N. Luke et al., entitled “A CdZnTe Coplanar-Grid Detector Array For Environmental Remediation”, Nuclear Instruments And Methods In Physics Research A 458 (2001) 319-324.
While the performance of radiation detector 1 shown in FIGS. 1 and 2 has been satisfactory, it would be desirable to provide a radiation detector device having improved performance.